1. Field of the Invention
The present invention relates to a testing apparatus for LEDs, and more particularly, to a testing apparatus which can measure flip chip LEDs and decrease the measuring errors at the same time.
2. Description of the Prior Art
Illumination system not only made positive progress in scientific and technological achievements, but also became a milestone of civilization. After the industrial revolution, humankind has begun to live in urban life due to the production intensification. Thus, the need of illumination is more necessary. There are a multitude of illumination devices well known and commonly used such as filament lamp, tubular fluorescent lamp, compact fluorescent tube, and high intensity discharge lamp. However, there is a common drawback to the illumination devices mentioned above: inefficient energy conversion. Therefore, developing more efficient illuminant is helpful to solve the energy shortage of the world.
Light emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting. In recent years, it is expectable to improve the luminous efficiency of illumination system due to the decrease of manufacturing cost and the increase of brightness for LEDs. Further, LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. Thus, LEDs have become very popular in recent years and will become major trend in the future.
So far, there are three main classes of the LED chip: horizontal type, vertical type, and flip chip. Wherein the electrodes of the horizontal type are configured on the light-emitting layer, resulting in a decrease of the light emitting area by the electrodes, and reduce the luminous efficiency. Likewise, the vertical type has the same problem. But the flip chip is different, because the electrodes and the light-emitting layer are configured on the two opposite faces of the substrate respectively. In other words, the electrodes have no effect on the light-emitting layer, therefore, flip chip LEDs have relatively high luminous efficiency.
Before applying LED chips to practice, inspection for adequacy is necessary. During the process of testing, the wafer of the LED chips is deposited on a carrier of the testing apparatus, and the LED emits light when the probe module contacts the electrodes. Subsequently, the optical detector further converts an optical signal into an electrical signal, and the probe module can measure the electric property of LED at the same time. In general, the probe module is usually fixed, and the carrier can control the position of LED for contacting the probe module. Consequently, there is an adhesive tape or an adhesive between the carrier and the LED for making the LED immobile, avoiding the offset error of the gliding LED.
Because the electrodes and the light-emitting layer of flip chip LEDs are on the different faces, the testing apparatus of horizontal type and vertical type became inapplicable. Thus, it is necessary to design a new type of testing apparatus for flip chip LEDs. Please refer to FIG. 1A, FIG. 1A is a schematic diagram illustrating a carrier 1 of a testing apparatus for flip chip LEDs according to the prior art. As shown in FIG. 1A, the carrier 1 comprises a substrate 10 and a supporting member 12, wherein the substrate and the supporting member are made of the materials with high light transmission, and furthermore, the substrate 10 and the supporting member 12 formed a closed space. In addition, an extraction apparatus 14 can pump air out of the closed space. The supporting member 12 includes a plurality of vent holes 120, when the extraction apparatus 14 pumps air out of the closed space, it will generate negative pressure through those vent holes 120, and make a transparent carrier 16 of the supporting member 12 fixed. Wherein, a flip chip LED 2 can be fixed on the transparent carrier 16 by using the adhesive tape or other adhesives. Hence, the light emitted by the flip chip LED 2 can penetrate the transparent carrier 16, the supporting member 12, and the substrate 10, and then be detected by the optical detector.
However, as the testing apparatus mentioned above, the vent holes 120 affect the results of testing. Please refer to FIG. 1B, FIG. 1B is a schematic diagram illustrating a flip chip LED fixed on the supporting member according to the FIG. 1A. As shown in FIG. 1B, the position of the transparent carrier 16 near the vent holes 120 generate deformation resulting from the negative pressure, and further, it causes the deflection of the flip chip LED 2. Due to the deflection of the flip chip LED 2, the results of testing will be inaccurate with measuring error. Therefore, the flip chip LED 2 near the vent holes 120 must be tested again but away from the vent holes 120. At the same time, the plurality of vent holes 120 should be widely distributed on the supporting member 12 in order to maintain the transparent carrier 16 fixed on the supporting member 12. In other words, the testing apparatus for flip chip LEDs mentioned above causes over much resource consumption for further development of the flip chip LEDs.